Transposition error protection system for telegraph signals



A ril 30. 1968 H. c. A. VAN DUUREN 3.331,27

TRANSOSITION ERROR PROTSCTION SYSTEM FOR TELEGRAPH SIGNALS Filed May a,1964 4 Sheets-Sheet l H fz f: h. fs fa 17 o o o o o x o 0 x x o o x o o0 o x x o o o n x o x o 0 o x o x o o o x x x o o o 0 x x o o o x x x xx x x x o x o o o o o o o o x o 0 x x o o x o o o o x x o o n o x 0 x oo o x u x o o o x x x o o o o x x o o o x b o x x o o x o INVENTOR. H.C. A. VAN DUUREN ATTORNEY TRANSPOSITION ERROR PROTECTION SYSTEM FORTELEGRAPH SIGNALS 4sheets-Sheet 2 Filed May 8, 1964 a b c d e nxxx xooo

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TRANSPOSlTlON ERROR PROTBCTION SYSTEM FOR TELEGRAPH SIGNALS 4Sheets-Sheet 3 Filed May 8, 1964 v OE muktmzxxmb a n 522410 UZwDOmu mwoo mmEou J .DUwzO mOFdwZmO 44205 NQ ATTORNEY April 1968 H c. A. VANDUUREN 3,38l,27l

TRANSPOSITION ERROR PROTECTION SYSTEM FOR TELEGRAPH SIGNALS 4Sheets-Sheet 4 Filed May a, 1964 No ao INVENTOR H. C. A. VAN DUURENATTORNEY H n zz GME zomu United States Patent O M 3,381,271TRANSPOSITION ERROR PROTECTON SYSTEM FOR TELEGRPH SIGNALS HendrikCorneiis Anthony van Dnnren, Wassenaar, Netherlands, assignor to DeStaat der Nederlanden, ten Deze Vertegenwoordigd Door de Directenr-Generaal der Posterijen, Telegrafie en Telefonie, The Hague, NetherlandsContiuuation-in-part of application Ser. No. 187,566, Apr. 16, 1962.This application May 8, 1964, Ser. No. 365,898

12 Ciaims. (Cl. 3413-1461) ABSTRACT OF THE DISCLOSURE A system forpreventing transposition errors in a twoway telegraph system comprisinggenerating a parity check signal for each block or group of lines ofbinary code telegraph sgnals. This system includes a transmitter and areceiver at each station each of which has a storing means, a repetitiondevice, and a counter means for generating and detecting, respectively,a parity check signal for the lines of multi-element code signals ineach block or group. If desired, each transmitter and receiver mayinclude also a code converter for converting each multi-element signalinto a Constant-ratio binary code multi-element signal for further errordetection. The lines of each block or group of signals for generatingthe parity check signal, may be taken from parallel rows, columns,and/or diagonals of either the original or the code converted signals.

This application is a continuation-in-part application of Van Duuren scopending U.S. patent application Ser. No. 187,566, filed Apr. 16, 1962,which claims priority from Netherlands application Ser. No. 264,766filed May 15, 1961.

Background of the invention Previously, protection against faultyreception has been achieved by 'working with Constant ratios of signalelements of different natures in the signals transmitted. Systems ofthis type proved susceptible to a particular kind of error consisting inthe falling out of a marking element and the simultaneous appearance ofa marking element, instead of a spacing element, in another place. Sucha transposition cannot be detected by these Well known protectionsystems.

Summary of the invention Generally speaking, the telecommunicationsystem of this invention is for protection against slipping in of errorsdue to transposition in multi-element code signals transmitted betweenat least two Stations in a network, each of which Stations has anassocated transmitter and receiver for two-way communication. Besidesthe necessary circuits for telecornmunication of the signals, eachtransmitter and receiver at each station comprises: a separate inputCircuit for each element of each signal transmitted and received, astoring means for a predetermined number of signals usually at least thenumber contained in a block or group of signals which s parity checkedaccording to the system of this invention, sepa Iate conductor meansbetween each input circuit and the storing means, and a repetitiondevice for controlling the storing means.

The improvement of this invention is characterized by counter means ineach transmitter and receiver, which counter means are connected to eachconductor means for counting the number of elements of a given type orpolarity in a predetermined number of signals which 3,38L27l PatentedApr. 30, 1968 form the group or block signals parity checked accordingto this invention. In combination with these counter means, means areprovided in each transmitter connected to the counter means at saidtransmitter for generating the Special, additional, Checking or paritysignal indicating the odd or even number of marks or Spaces in'particular columns, rows, or diagonal lines of elements in said block.Then also at each receiver there is provided means connected to each ofthe counter Circuits for comparing, testing or checking the paritysignal against the corresponding elements counted in the same columns,rows or diagonal lines of the block of signals received, to insure thatthe block was not erroneously received. If an error is detected theassociated repetition device is signalled to request repetition of thatblock of signals until it is properly received. The re-transmission ofthe block of signals from the storing means in the transmitter alsoincludes the retransmission of its associated parity signal.

In addition to the above basic Circuits of this invention there also maybe employed in each transmitter and receiver a plurality of gate means,including OR gates, in each of said conductor means, and a pulsegenerator means for controlling the said gate means for permittingpassing and spacing of the elements of the signals as they pass throughthe Circuits in the proper sequence and order, whereby the groups orblocks of signals may be counted and spaces left between them for thetransmission of the Special, Checking, or parity signals. Furthermore,each transmitter and receiver may also include a code converter means,if each of the signals is to be converted into a constant mark/ spaceratio signal for further checking each of the signals, as Well as theblock of signals parity checked according to the'circuits of thisinvention. In such a case, the receiver circuits include a signal ratiotester circuit for Checking this constant ratio, which tester circuit isconnected to the repetton device so that erroneously received signalscould be requested by repetition.

Still further, the system of this invention may comprise a multi-channelsystem in which each one of the elements of each signal beingtransmitted may be transmitted on a separate signal Channel and/ or at adiferent frequency for further insurng protection against errors.

(a) Objecls and advantzzges Accordingly it s an object of this inventionto provide a system for the prevention of transposition errors.

Another object is to produce such a system by checking groups ofelements in a predetermined number, group, or block of signals.

Another object is to produce such a protection system by transmitting achecking or parity signal after each checked group or block of signalsor signal elements.

Another object is to produce such a system in which the signals arechecked at least twice for a constant ratio of mark/space elements,namely for each message signal and for each block or group of signals,and may also be further checked by Checking the parity signal either ofconstant mark/space ratio, or with an additional checking elementtherein, or both.

Brief description of the drawngs The above mentioned and other featuresand objects of this invention and the manner of attaining them willbecome more apparent and the invention itself will be understood best byreference to the following description of embodiments of the inventiontaken in conjunction with the accompanying drawings, wherein:

BIG. 1 discloses ch-arts of a group of four five-element message signalstogether with a parity signal derived therefrom according -to oneembodiment of .the system of this invention, plus (at the right) a groupof Seven-element constant ratio mark/space code signals converted fromthe block of five signals at the left;

FIG. 2 discloses charts similar to FIG. 1, but with the parity signalderived from the first six elements of the Constant ratio code convertedsignals, plus a final or seventh self-checking element according toanother embodiment of the system of this invention;

FIG. 3 is a code conversion table between the five-element signals andconstant 'ratio seven-element signals shown in the charts of FIGS. 1 and2;

FIG. 4 is a. schematic block wiring diagram of a transmitter circuit forproducing the groups or blocks and parity sign-als according to theembodiment shown in FIG. 1;

FIG. 5 is a time diagram of the pulse waves employed for controlling thetransmitter circuit shown in FIG. 4;

FIG. 6 is a schematic block wiring diagram of a receiver circuit forreceiving the groups and parity signals shown according to the charts ofFIG. 1 and transmitted by the circuit of FIG. 4;

FIG. 7 is a time diagram of the pulse waves employed in controlling thereceiver circuit shown in FIG. 6; and

FIG. 8 is .a chart of a group or block signals including a parity signalderived according .to .a still further embodiment of this invention,showing three eight-element message signals and one eight-element paritysignal derived from the three message signals by diagonal lines .throughtheir block of elements.

- Detailed description of preferred embodments (I) THE SIGNALS Themulti-element signals communicated by this invention all have the samenumber of elements per si-gnal, so that a group thereof forms a block ofelements in rows and columns from which the parity or checking signal isproduced. The parity signal is co-mposed of elements determined from thenumber of elements of like order in each line, column, row, or diagonalof elements in such a block. For example, none or an even number ofmarking elements in a line may be indicated by a mark element in acertain element position in the parity sign-al, whle an odd number ofmarking elements in that line would be indicated by a space element.Then each element position in the parity signal contains an element fora different line row, or column in the block, or an element based on thenumber of marks in the rest of its own signal. This invention, however,is not limited to just mark and space criterions, in that separatefrequencies can be employed for each element and/or its position in eachsignal, or in each block.

However, for the purposes of illustraton hcrein, reference is first hadto FIG. 1 which shows charts of two 'blocks of signals, the one at theleft comprising four horizontal rows of four five-element telegraph codemessage signals, such as according to the Baudot Code, each of the fivevertical columns in which block contains an even or no marking elementsX, which s indicated by a mark at the bottom of each column to make upthe five-element parity signal across the bottom of the block under thehorizontal line, which block of five fiveelement signals is transmittedby the system of this invention. At the right half of FIG. 1, the fiverows of signals are shown converted into .a seven-Unit code in whicheach signal or horizontal row of elements contains a constant ratio of-marks and Spaces, namely three marks and four Spaces, ineluding theelements in the parity signal. This block of five rows and seven columnsof elements is then transmitted so that not only is each signal .thereofcheeked along the rows for constant ratio, but after the block isreconverted back into the five-element signals shown at the left of FIG.1, the number of marks in each column are also checked or compared todetermine if they correspond with the reconverted parity signal, at thebottom of this five-element block. It sh'ould be noted in thisembodiment of the invention, that the converted parity signal underneaththe horizontal line in the right-hand block in FIG. 1 does not containelements which correspond with the number of marks or Spaces n thecolumns fl through f7.

In FIG. 2 there is shown by charts of blocks of elements how .anothertype of parity signal may be produced employing the same fourfive-element signals in the left hand block as shown in FIG. 1, butconverting these four signals into the seven-element constaut ratio codebefore producing the parity signal, so that the parity signal is derivedfrom the block of seven-element signals. For example, the first sixVertical columns of elements in the seven-element code are employed formaking up the first Six-elements of the parity signal shown in row b.Then the last or seventh element in the row b is determined from the oddor even number of mark elements in the six elements already formed inthe parity signal, to act as a further check element for the paritysignal b itself. Also this seventh element may be used to insure aConstant mark/space ratio for the parity signal. Thus according to FIG.2, the block of the thirtyfive elements eomprises five seven-elementsignals, for which the parity check or test is made before theconversion at the receiver of the first four or message signals intotheir five-element code signals.

In FIG. 3 there is shown a conversion table for thirtytwo, 0 through 31,five-element code signals in columns A through E in to theircorresponding seven-element constant ratio code signals in columns athrough g, and vice versa. According to the 3/4 mark/space combinationsand permutations of seven elements, thirty-five different signals arepossible, which is three more than in the 5 five-element code, whichthree additional signals .are shown at the bottom of these columns athrough g as Special signal I and idle time signals a and 5. Inre-converting .these .three .additional signals back to the originalfive-element code, they have been so chosen that out of the list ofalready existing thirty-two signals they can only be confused with theone other similar signal, if as many transpositions as possible occurein the sevenelement signal. Thus only double transpositions in eachsignal during the transmission of these three seven-element signalscould cause them to 'be confused with their similar convertedfive-element signals, which eTects further protection against errors.

(II) THE TRANSMITTER Referring now to FIG. 4 there is shown a schematicblock wiring diagram of a transmitter circuit for one of the Stationsfor the transmission of four information signals plus a parity test orChecking signal in accordance with the blocks of elements disclosed inFIG. l. The five elements of the four information or message signals areread simultaneously from the taipe reader TR shown at the left end ofFIG. 4, triggered by a pulse from pulse generator P *1 through AND gateGP 1 in combination with a potential from the repetition device TRDindicating that a repetition is not being requested through conductor40. The information from each of the five elements on the tzupe is thentransmitted, such as through the feeler switches S 1 through S 5, to thecorresponding bistable triggers C 1 through C 5 until changed by afollowing different impulse from the tape reader TR are applied to them.

The information from these triggcr Circuits C 1 through C 5 is thentran'smitted through conductors 41, 42, 43, 44 and 45, respectively, toAND gatos GC 1, GC 2, GC 3, GC 4 and GC 5, controlled by a pulse frompulse generator P 2 through AND gate GP 2, right after completion ofoperation of pulse P 1, as indicated by the pulse waves P 1 and P 2shown in FIG. 5. AND gate GP 2 is also controlled by the repetitiondevice TRD, so that when a repetition is not being requested, the thenConstant potential iu conductor 40 also is applied to the GP 2.

Connected also to the conductors 41 through 45, respectively, aresepara'te counter circuits T 1 through T 5 which make up part of theChecking or parity signal generator circuit PSG. According to FIG. 1these counters T 1 through T 5 count if the num er of mark e lementsoccurring for four signals in its corresponding column, position orconductor is odd or even, to produce a space or mark element,respectively, in that position for the parity signal. The final outpu-tsof each of these counters T .1 through T 5 are passed through AND gatesGT 1 through GT S, respecti vely, by a pulse fro-m generator P 3 throughAND gate GP 3, also controlled as gates GP l and GP 2 by the potentialin conductor from the repetition device TRD. This pulse P 3 (see Waveforms in FIG. 5) occurs after all four message signals making up thegroup or block have been passed through the code converter TCC via ANDgates GC 1 through GC 5 and OR gates OG 1 through OG 5. This codeconverter TCC comprises logic circuits for converting the five elementcode signals into seven element code signals having a constant mark/space ratio according to the table shown in FIG. 3. -Also connected tothese OR gates OG 1 through OG 5, respectively, are the outputs of theAND gates GT 1 through GT 5 of the parity signal generator circuit, sothat then under the control of pulse P 3 the proper parity signaldetermined by the counters T 1 through T 5 is passed to the codeconverter TCC completing the block .of five signals shown at the left inFIG. 1.

From the code converter TCC extend seven conductors 51 through 57connected both to the five signal storing device TM and to the sevenseparate outpnt triggers K 1 through K 7, which may be transmitted overseven separate frequencies of seven separate signal Channels. Thus allfive-element signals are converted into seven element signals which areboth stored and passed for transmission each group cycle of the systemunder control of the pulses from generator P 3. Although such a codeconverter TCC is not necessary according to the block checking system ofthis invention, it is necessary if the additional constant ratio test ofeach one of the signals in the block is also to be provided.

In the event an error occurs and a repetition is required, therepetition device TRD connected through conductor 40 to the gates GP 1,GP 2. and GP 3, also is connected via conductor 58 to the outputs .ofthe Storage device TM to permit repetition of the five seven-elementsignals of the block last recorded therein and also to cut oif thepotential applied via conductor 49* to block further signals from beingread in the tape reader TR by pulse P 1 via Gate GP 1, to block transferof signals stored in the input trigger C 1 through C S from beingtransferred to the code converter TCC by pulse P 2 via gate GP 2, and toprevent parity signals generated in the counters of T 1 through T 3 frombeing passed to the code converter TCC, all until the repetition deviceTRD has been re-set. Furthermore, in order to simultaneously record thefive Converted signals in the memory Circuit TM, the pulse generators P2 and P 3 are also connected through OR gate OG 6 to the memory deviceTM for controlling the internal operation or stepping thereof for thesequential storing of these five signals making up the block, as theyare Converted from the .output conductors 51 through 57 from the codeconverter TCC.

As seen from the time diagram in FIG. 5, the reading by pulse P 1 andcode conversion by pulse P Z lasts four times ten milliseconds, followedby the transmission of the parity test signal controlled by pulse P 3which lasts ten milliseconds, then the process is repeated after a pauseof 510 milliseconds, thus permitting time for the reading and conversionof the six other signals of the seven message Channels No. 1 through No.7 with which the seven elements of each converted signal areinterspersed at difierent frequencies from triggers K 1 through K 7 inFIG. 4.

6 (III) THE RECEIVER In FIG. 6 is shown a schematic block wiring diagramof a receiver circuit for receiving the five seven-element signals shownat the right in FIG. 1 and transmitted by the transmitter Circuit ofFlG. 4, and reconverting them back into the block of five five-elementsignals shown at the left in FIG. 1 for parity Checking.

The seven input or receiving bista ble triggers R 1 through R 7,correspond to the seven diiferent elements of each signal received, andmay correspond to the seven different frequencies of the seven differentChannels No. 1 through No. 7 by which the seven elements of each signalis transmitted as shown in FIG. 4. From the output of each of theseseven triggers R 1 through R 7 there are provided separate conductors 61through 67, each of which are connected both to separate AND gates G 1through G 7, respectively, as well as to the ratio tester Circuit RT fortesting the Constant mark/space (3/4) ratio of all seven of the elements.of each one of the signals.

If the ratio is tested to -be proper, no potential is passed through ORgate G 8 to the repetition device RRD. However, if on the other hand,one of the signals has been tested to be mutilated or in error, then therepetition dvice RRD is operated which in turn via conductor 79 operatesthe local transmitter repetition device TRD (see FIG. 4) to request arepetition of the last signal block. Also at this time potentialnormally applied from the repetition device RRD in conductor 71 is cutoff to the AND gate AG 13, which prevents any pulses from pulsegenerator P 13 (see also time diagram in FIG. 7) via conductor 72, frompassing any stored signals from the output of the memory device RM, suchas to a printer.

The conductors 61 through 67 from the input triggers R 1 through R 7also pass each element of each signal as it is received to the gates G 1through G 7 which gates are triggered by pulses from pulse generator P11 (see also time diagram of FIG. 7), via conductor 73. This pulse P 11permits the elements indicated on the triggers R 1 through R 7, afterthey have been tested by the radio tester RT, to be passed to the codeconverter RRC and converted back through logics into the five-elementcode signals shown at the left n FIG. 1 according to the table in FIG.3, and are produced on the out-put conductors 81 through S5 'from theconverter RRC. Since it is this five-element code which had its elementscounted to produce the Special Checking or parity signal each of theseconductors S1 through S5 are connected not only to the four five-elementsignal Storage or memory device RM, but are also connected to a paritysignal Checking Circuit PSC of the separate counters TT 1 through TT 5which count the number of rnarks in each element position of the foursuccessive signals making up the block of signals transmitted. At thistime each of the counters TT 1 through TT 5 are in a definite positionfor comparison purposes with the elements of the fifth, Checking, orparity signal. Thus, if the counters TT 1 through TT S are not changedin their said definite positions by the elements of this fifth or paritysignal, the block of tour signals counted was correctly received, and noimpulse will be passed from any of the counters TT 1 through TT 5through OR gate OG 9 to AND gate AG 12. If, however, even one of theelements of the parity signal does not compare with the positions ofthat one of counters TT 1 through TT 5, an error has occurred and animpulse is passed through OR gate OG 9 at the same time a pulse from thepulse generator P 12 (see also FIG. 7) via conductor '74 is applied tothe AND gate AG 12 to operate the repetition device RRD. This thencauses a request via conductor 70 for the repetition of the lastreceived block of signals, While preventing transfer of any storedsignals from the memory device RM via conductor 71 and AND gate AG 13.

7 IV MODIFICATIONS In adapting the circuits shown in FIGS. 4 and 6 for aset of signals corresponding to that shown in FIG. 2, wherein the paritysignals are produced from the signal after it has passed through thecode converter, substantially all that needs to be done is to Connectthe parity signal generator circuit PSG in the transmitter of FIG. 4 tothe conductors 51 through 57 instead of to the conductors 41 through 45as shown, and correspondingly connect the parity signal Checking circuitPSC in the receiver of FIG. 6 to the conductors 61 through 67 instead ofto the conductors 31 through 85 as shown. This would require anadditional two counters in each circuit PSG and PSC for the additionaltwo elements in the signals; and according to the parity signal b inFIG. 2 the sevcnth counter will be connected to the previous sixcounters for forming the seventh element therefrom as previouslydescribed in section I above.

In FIG. 8 there is shown charts of three message signals and one paritysignal of eight elements each arranged in a block according to stillanother cmbodiment of the principle of this invention. In thisparticular embodiment eight different marking and spacing frequcnciesare eniployed, which may be transmitted simultaneously, in each of theeight different signal Channels. Thus, there is a choice of twofrequencies in each Channel lying about 100 cycles apart, one for marksand the other for Spaces, with the center frequencies of each channelbeing spaced 200 cycles apart. In the chart in FIG. 8, the elements incolumns 2 through 6 and rows I through III correspond to the elements ofthe three five-unit message code signals transmitted. Before eachmessage signal in column 1 is added an element (circles with center dot)which may have the same polarity, and added two elements after each mes-2 sage signal (sqnares with center dots) in columns 7 and S representthe parity tests on the groups of preceding elements in the same row,namely; element 7 is produced from the elements 1, 3 and S in that row,and element 8 is produced from the elements 2, 4 and 6 in that row. Thebase of the block in FIG. 8, is shown an eight element parity signal(triangles with center dots) based on the elements along the diagonallines shown in FIG. 8, for example, the first element of this paritysignal is produced from the number of marks in the three row-columnelement positions of I-3, II-S and III-7; etc., When the diagonal linesin the group do not have three elements in a straight line, they areconnected around to the corresponding other ones of the matrix, group orblock as shown by the arrowed lines in FIG. 8. Thus correlation betweenerrors rendered in these sum tests is reduced by the frequency jumpsbetween the successive letters, since it is not very probable that anerror in unit or element or column 1 of the letter row I will coincidewith an error in unit or column 3 of letter II, or unit in letter III.Thus this diagonal test contrasts favorably with the vertical testsdisclosed in FIGS. 1 and 2 and described above.

The element in column 1 can serve to form signal groups, and also mayhave a marking polarity, for example, for all the letter signals, sothat if the first element has a spacing polarity the group following inthe rows are service signals thereby having the possibility of producing32 different service signals.

Thus this particular adaptation has additional double Checking features,and the Checking of the elements of the different columns, rows,diagonals, etc. depends upon where the counters of the parity signalgenerating and checking circuits PCG and PCC, are connected; that is towhich conductors, between the element input circuits and the memorydevices in each receiver and transmitter, the counters are connected,and to which, if any counters are connected to other counters. Thus,many different testing and parity checking systems can be provided forblocks or groups of elements and signals according to this invention.

While there is described above the principles of this invention inconnection with specific apparatus, it is to be clearly understood thatthis description is made only by way of example and not as a limitationto the scope of this invention.

What is claimed is:

1. In a telecommunication system for multi-element code signals betweentwo Stations, each station having a transmitter and a receiver and eachtransmitter and receiver comprising:

(A) separate input circuits for each element of each signal,

(B) a storing means for a predetermined number of signals,

(C) conductor means connected between each input circuit and saidstoring means, and

(D) a repetition device for controlling said storing means, theimprovement comprising:

(l) a counter means in each receiver and transmitter connected to eachconductor means for counting the number of elements of a given typealong a predetermined line of a predetermined number of signals forminga block,

(Z) means in each transmitter connected to said counter means in thattransmitter for generating a parity signal corresponding to the elementsin said block for transmission after said block, and

(3) means in each receiver connected to said counter means in thatreceiver for comparing said parity signal against the correspondingelements counted in said block of received signals, and controlling saidassociafed repetition device in accordance therewith, so that erroneousblocks of signals will be requested to be repeated until receivedcorrectly.

2. A system according to claim 1 including (E) gate means in each saidconductor means, and

(F) pulse generating means for controlling said gate means, and whereinsaid means in each transmitter for genera-ting said parity signal iscontrolled by its 'associated pulse generating means, and wherein saidrepetition device in each receiver is controlled by said pulsegenerating means.

3. A system according to claim 2 wherein said gate means .includes ANDga'tes in each transmitter and receiver connected to each conductormeans.

4. A system according to claim 1, including:

(4) a first code converter means connected to said conductor means ineach transmitter in a predetermined way for converting saidmulti-element code signals into code signals of Constant ratio of marksand spaces, and

(5) a signal ratio test means connected to said conductor means in eachreceiver.

5. A system according to claim 4 including:

(6) a second converter means connected to said conductor means in eachreceiver for converting said constant ratio code signals back to saidmulti-element code signals.

6. A system according to claim S wherein said first code converter meansin said transmitter is connected to said conductor means after saidcounter means, and said second converter means in said receiver isconnected to said conductor means before said counter means.

7. A system according to claim 1 wherein said system 'comprises amulti-channel system with a different channel corresponding to eachelement of the multi-element code signal transmitted between saidstations.

8. A system according to claim 1 wherein said multielemen't signalscomprise binary elements corresponding to mark and space indications,and wherein the elements of said parity signal corresponds to the numberof marks in predetermined lines of elements in said -block of signals.

*9. A system for protecting against transposition errors inmulti-element signal telecommunications between at least two stations,each .station having a transmitter and a receiver;

(A) each transmitter comprising:

(1) a multi-element signal input device,

(2) a Storage device for a predeter-mined plurality of saidm-ult-element signals consisting of a group of message signals plus aparity signal,

(3) separate conductors for each element of said signal between said'input device and said storage device.

(4) a separate counter connected to each conductor for counting thenumber of elements of a given type along predetermined lines of saidgroup of signals,

(5) means to generate a parity signal determined by said Counters,

(6) means for transmitting said group of signals fol-lowed by saidparity signal to the receiver at a remote station, and

(7) a repetition device controlled by the receiver at the same stationand connected to said Storage device for repeating said group of signalsand said par'ity signal stored in said storing device; and

(B) each receiver comprising:

(1) means to receive each element of said multielement signalstransmitted from a remote station,

(2) a memory device for said group of message signals, v

(3) separate conductor means for each element of said multi-elementsignal between each said receiving means and said memory device,

'(4) a separate counter connected to said conductor means for countingthe number of elements of said given type along said prede'terminedlines of said group of signa'ls,

(5) means connected between said Counters and said repetition device forcomparing said counters with said parity signal, and

(6) a repetition requesting device controlled by 'said comparison meansto control the repetition device in -the transmitter at that station.

10. A system for protecting against transposition errors inmulti-element signal telecommunications between at least two Stations,each station having a transmitter and a receiver;

(A) each transmitter comprising:

(1) a multi-element signal input device,

(2) a Storage device for a predetermined plurality of said multi-elementsignals consisting of a block of message signals plus a parity signal,

(3) separate conductors for each element of a signal between said inputdevice and said storage device,

(4) a gate in each said conductor,

(5) a pulse generator means for controlling said gates,

(6) a code converter for converting each signal of said group into asignal of a Constant ratio of marks and Spaces, and controllcd by saidpulse generator means,

(7) a separate counter connected to each said conductor for counting thenumber of elements of a given type along predetermined lines of saidgroup of signals,

(8) means controlled by said pulse generator to generate a parity signaldetermined by said Counters,

(9) means for transmitting said group of signals followed by said paritysignal to the receiver at a remote station, and

(10) a repetition device controlled by the receiver at the same stationand connected to said Storage device for repeating said group of signalsand said parity signal stored in said storing device; and

each receiver comprising:

(1) means to receive each element of said multielement signaltransmitted from a remote station,

(2) a memory device for said groups of message signals,

(3) separate conductor means for each element of said multi-elementsignal between each said receiving means and said memory device,

(4) means connected to said conductor means to test the ratio of markand space elements in each signal,

(5) code converter means for converting said constant ratio code signalsback into the multielement code signals,

(6) a pulse generator means for controlling said memory device and saidcode converter means,

(7) separate counter means connected to each conductor means forcounting the number of elements of said given type along saidpredetermined lines of said group of siganls,

(8) a repetition requesting device controlled by the said ratio testerto control the repetition device in the transmitter at that station, and

(9) gate means connected between said counter means and said repetitiondevice for comparing the results of said Counters with said -paritysignal also for controlling the operation of said repetition requestingdevice.

11. A system according to claim 10 wherein said code converter in saidtransmitter is connected to said con ductor means after said countermeans, and wherein said code converter means in said receiver isconnected to said conductor means before said counter means.

12. A system according to claim 10 wherein said telecommunication systemcomprises a multi-channel system, and the number of Channels correspondsto the number of elements in the code signals transmitted between saidStations.

References Cited UNITED STATES PATENTS 3,005,871 10/1967 Rudolph 178--263,147,460 9/1964 Scott 340 146.1 3,242,461 3/1966 Silberg et al.340-146.1

MALCOLM A. MORRISON, Primary Examiner.

C. E. ATKINSON, Assistant Examiner.

